This invention relates to a retracting sootblower for boiler cleaning and in particular to a method and apparatus for preheating the sootblower lance prior to supplying a blowing medium to the lance in the form of vapor, such as steam, to prevent condensation of the blowing medium in a cooled lance.
Sootblowers are used to project a stream of blowing medium such as air or steam against heated surfaces within boilers to cause slag and ash encrustations to be removed. The blowing medium impact produces both mechanical and thermal shock which causes these adhering layers of slag and ash to be removed. One general category of sootblowers is known as the retracting type. These devices have a retractable lance which is periodically extended into and retracted from the boiler such that one or more nozzles at the distal end of the lance project a jet of the blowing medium within the boiler. During extension and retraction, the lance may also be rotated or oscillated about its axis.
During the intervening time between sootblower operating cycles with the lance at rest outside of the boiler, the lance will cool to the ambient temperature of the air surrounding the boiler. During operation of a sootblower, as the lance is extended into the boiler, the flow of the blowing medium is initiated so that along a path traced by the blowing medium, encrustations from the boiler internal surfaces are removed. When the lance reaches its full extension into the boiler, its direction of travel is reversed and the lance is retracted from the boiler.
However, due to the cooling of the lance between operating cycles, when the lance is first extended into the boiler at the beginning of the next cleaning cycle and the blowing medium is supplied to the lance, the colder lance temperature results in partial condensation of the blowing medium vapor. The projection of the liquid condensate against the internal boiler surfaces increases the erosion of these surfaces. Erosion of boiler internal surfaces due to condensate is generally noted on the surfaces impacted by the blowing medium during the first one or two feet of extension of the lance into the boiler. After this initial lance travel, the lance will have been heated by the blowing medium and boiler gases such that condensate is no longer formed.
It is an object of the present invention to provide preheating of the lance prior to introduction of the blowing medium into the lance, thereby avoiding the cooling of the blowing medium by a colder lance to prevent condensation of the blowing medium.
It is a feature of the present invention that the lance is preheated by hot combustion gases within the boiler thus requiring no additional energy expenditure to heat the lance. Preheating is accomplished by delaying supply of blowing medium during lance extension into the boiler. The blowing medium is provided only after the lance has been heated to a predetermined temperature. As a result, when the blowing medium ultimately is provided, no condensation is produced.
Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from the subsequent description of the preferred embodiments and the appended claims taken in conjunction with the accompanying drawings.